Power law approximations to gas volume fraction and velocity profiles in low void fraction vertical gas-liquid flows

A dual sensor conductance probe was used to measure the distributions of the local gas volume fraction and the local gas axial velocity in vertical upward, bubby air–water flows in which the mean gas volume fraction was less than 0.1. Very limited data are available in the literature for such low volume fraction flows. The measured local gas volume fraction and velocity distributions were approximated by power law functions. The power law exponents associated with the measured local gas volume fraction profiles were found to be up to 30% higher than values predicted in the literature. The power law exponents associated with the measured local gas velocity profiles were also found to be somewhat higher than values predicted in the literature. The power law exponents for the measured local gas volume fraction and local axial gas velocity distributions at a given flow condition were combined to obtain an estimate of the ‘Zuber–Findlay’ distribution parameter C0 at that flow condition. The mean value of C0 for all of the flow conditions investigated was 1.09. This value of C0 was found to give good agreement with the gradient of a plot of the mean gas velocity versus the homogeneous velocity uh, where and uh were obtained from reference measurements. This agreement is evidence for the good accuracy of the measured volume fraction and velocity profiles. Finally, the paper casts doubt upon previously published criteria regarding the optimum axial sensor separation in dual sensor probes.